Will the M1 MBP support a USB 3 external monitor, sidecar and a webcam (hdmi to USB camlink) simultaneously?

Pundits have take the 'limited to ONE external display' statement as a challenge to hook up as many hacks as possible, and discovered that DisplayLink software and Docks can provide several additional displays, but these are slightly less capable than Apple's 'full-motion video with no dropped frames' standard for Hardware-accelerated displays.

Similarly, Sidecar does not provide a full motion video standard display, but most users do not expect it to provide that level of display on their iPad. Its video is compressed.

Sidecar does not use rasterizer/display-generator hardware (of which the Apple-silicon M1 MacBook Pro has only ONE available).

Yes, that will work. You’d need a USB-C-to-A adapter for the CamLink.

@Grant, the CamLink (assuming the OP means the Elgato product) is a video capture card in a dongle format, HDMI in from the camera, USB out to the computer.

Thanks for that clarification. that helps me understand and I drop nay objections, that setup should work.

I was just stuck on a thread where the user was baffled that their HDMI-USB cord was not working.

It turned out that they had connected it to the HDMI output of the Mac, expecting it to convert to USB for the outboard display device. Malcolm J Rayfield bailed me out by pointing out the adapter/cables did not work with HDMI source, USB destination.

You can not connect a cable that is HDMI at the 'smart' end to another type of port.

Yes, the M1 Mac notebooks support only one external display, but yes you can still use Sidecar for an additional display along with an external monitor for three desktops.

Your workflow will work.